Ni No Kuni 2 - Tainted Monster #50 Boss Fight:

Ni No Kuni 2 - Tainted Monster #50 Storme Boss Fight for trophy "Scourge of the Tainted" (Tainted Monsters List with their locations at end of video).

There are 60 Tainted Monsters in Ni No Kuni 2 Revenant Kingdom. The last 10 only spawn after having defeated the first 50.
Luckily, for the trophy you only need 50/60. Do everything in the game and you'll be level 75 or so. Below this level it will be hard to beat the boss. At level 75 it's not too difficult.